Posterior dynamic stabilization x-device

ABSTRACT

Various methods and devices are provided for stabilizing the posterior elements of the spine, and more preferably methods and devices are provided for sharing the load with the intervertebral disc, the facet joints, the ligaments, and the muscles of the spinal column. In certain exemplary embodiments, methods and devices are provided for substantially controlling or providing resistance to movement, e.g., flexion, extension, lateral bending, and/or axial rotation, of the adjacent vertebrae.

BACKGROUND OF THE INVENTION

The vertebrae in a patient's spinal column are linked to one another bythe disc and the facet joints, which control movement of the vertebraerelative to one another. Each vertebra has a pair of articulatingsurfaces located on the left side, and a pair of articulating surfaceslocated on the right side, and each pair includes a superior articularsurface, which faces upward, and an inferior articular surface, whichfaces downward. Together the superior and inferior articular surfaces ofadjacent vertebra form a facet joint. Facet joints are synovial joints,which means that each joint is surrounded by a capsule of connectivetissue and produces a fluid to nourish and lubricate the joint. Thejoint surfaces are coated with cartilage allowing the joints to move orarticulate relative to one another.

Diseased, degenerated, impaired, or otherwise painful facet jointsand/or discs can require surgery to restore function to the three jointcomplex. Damaged, diseased levels in the spine were traditionally fusedto one another. While such a technique may relieve pain, it effectivelyprevents motion between at least two vertebrae. As a result, additionalstress may be applied to the adjoining levels, thereby potentiallyleading to further damage.

More recently, techniques have been developed to restore normal functionto the facet joints. One such technique involves covering the facetjoint with a cap to preserve the bony and articular structure. Cappingtechniques, however, are limited in use as they will not remove thesource of the pain in osteoarthritic joints. Caps are alsodisadvantageous as they must be available in a variety of sizes andshapes to accommodate the wide variability in the anatomical morphologyof the facets. Caps also have a tendency to loosen over time,potentially resulting in additional damage to the joint and/or the bonesupport structure containing the cap.

Other techniques for restoring the normal function to the posteriorelement involve arch replacement, in which superior and inferiorprosthetic arches are implanted to extend across the vertebra typicallybetween the spinous process. The arches can articulate relative to oneanother to replace the articulating function of the facet joints. Onedrawback of current articulating facet replacement devices, however, isthat they require the facet joints to be resected. Moreover, alignmentof the articulating surfaces with one another can be challenging.

Accordingly, there remains a need for improved systems and methods thatare adapted to mimic the natural function of the facet joints.

BRIEF SUMMARY OF THE INVENTION

The present invention provides various methods and devices forstabilizing the posterior elements of the spine. In certain exemplaryembodiments, methods and devices are provided for controlling orproviding resistance to movement, e.g., flexion, extension, lateralbending, and/or axial rotation, at least two adjacent vertebrae. Incertain exemplary embodiments, the methods and devices are particularlyadvantageous in assisting the facet joints and posterior spinal musclesand ligaments in controlling motion in the lumbar spine, either with aderanged intact disc, with a nucleus replacement, or with a total discreplacement.

In one exemplary embodiment, a spinal stabilization device is providedhaving a central spacer with at least two arms extending therefrom andadapted to couple to adjacent vertebrae. The central spacer and the armscan have a unitary configuration and can be formed from an elastomericmaterial with multiple durometers. For example, a first portion of eacharm adjacent to the central spacer can have a durometer that is lessthan a durometer of the central spacer, and a terminal portion of eacharm can have a durometer that is greater than a durometer of the centralspacer. In one exemplary embodiment, the terminal portion of each arm issubstantially rigid to allow the arms to be coupled to vertebrae.

In another exemplary embodiment, a spinal stabilization device isprovided having a central spacer that is adapted to be positionedbetween posterior elements of adjacent vertebrae and that is adapted tolimit extension of the adjacent vertebrae. The device can also includeat least one pair of arms extending from opposed sides of the centralspacer and adapted to couple to a vertebra. At least a portion of the atleast one pair of arms can be pliable to control or provide resistanceto movement, e.g., flexion, extension, lateral bending, and/or axialrotation, of adjacent vertebrae coupled thereto. The arms and thecentral spacer can be of a unitary construction, or they can be fixedlyor removably coupled to one another. For example, in one embodiment atleast one of the arms can be slidably disposed through the centralspacer.

In another embodiment, the pair of arms can have a first portionadjacent to the central spacer and a second terminal end portion. Thefirst portion can be more pliable than the second terminal end portionto allow flexion of the adjacent vertebrae. Pliability, e.g.,flexibility, elasticity, etc., can be provided by, for example, a coiledportion formed on the arms. In another embodiment, the at least one pairof arms can be in the form of first and second arms extending fromopposed sides of the central spacer, a third arm removably coupled tothe first arm, and a fourth arm removably coupled to the second arm.

In another exemplary embodiment, the spinal stabilization device caninclude a first pair of arms extending from a first lateral side of thecentral spacer and a second pair of arms extending from a second lateralside of the central spacer. The first pair of arms can be integrallyformed within one another, and a second pair of arms integrally formedwith one another. In use, the first and second pair of arms can beadapted to mate to the central spacer at a variety of angularorientations.

In other aspects, a spinal stabilization device is provided having afirst pair of arms and a second pair of arms. Each pair of arms can havea superior portion adapted to mate to a superior vertebra, an inferiorportion adapted to mate to an inferior vertebra, and a central portionextending between the superior and inferior portions. The device canalso include a central spacer that is adapted to be positioned betweenposterior elements of adjacent vertebrae, and that includes across-connector extending therethrough and adapted to engage the centralportion of the first and second pair of arms. In an exemplaryembodiment, the cross-connector is slidably adjustable relative to thefirst and second pair of arms. The cross-connector can have a variety ofconfigurations, and it can include, for example, hook-shaped membersformed on opposed ends thereof and adapted to engage the central portionof the first and second pair of arms. Alternatively, the cross-connectorcan be in the form of a clamp having openings formed in opposed endsthereof for receiving the central portion of the first and second pairof arms and for engaging the arms when the clamp is in a closedposition.

In use, the first pair of arms extending from the central spacer can becoupled to a first lateral side of adjacent superior and inferiorvertebrae, and the second pair of arms extending from the central spacercan be coupled to a second lateral side of adjacent superior andinferior vertebrae. The central spacer can then be slid insuperior-inferior direction relative to the first and second arms toposition the central spacer as desired. Once properly position, thecentral spacer can be locked in a fixed position relative to the firstand second pair of arms.

In other aspects, the spinal stabilization device can include a firstpair of arms extending from the first lateral side of the central spacerand adapted to couple to adjacent superior and inferior vertebrae, and asecond pair of arms extending from the second lateral side of thecentral spacer and adapted to couple to adjacent superior and inferiorvertebrae. At least a portion of at least one of the first and secondpair of arms can be pliable to control or provide resistance tomovement, e.g., flexion, extension, lateral bending, and/or axialrotation, of adjacent superior and inferior vertebrae coupled thereto.While the first and second pair of arms can have a variety ofconfigurations, in one exemplary embodiment, the first pair of arms canbe coupled to one another and the second pair of arms can be coupled toone another, and the first and second pair of arms can be removablymated to the central spacer. In another exemplary embodiment, the firstpair of arms can comprise a first arm and a second arm, and the secondpair of arms can comprise a third arm and a fourth arm, and the first,second, third, and fourth arms can be independently removably mated tothe central spacer. The central spacer can include a first openingformed in the first lateral side and adapted to removably receive thefirst and second arms, and a second opening formed in the second,opposed lateral side and adapted to removably receive the third andfourth arms. First and second locking mechanisms can be disposed throughthe first and second openings for locking the first, second, third, andfourth arms to the central spacer.

In another exemplary embodiment, a multi-level spinal stabilizationsystem is provided. The system can include at least two X-shapedmembers, and each X-shaped member can have a central member with asuperior pair of arms extending from opposed lateral sides thereof andan inferior pair of arms extending from the opposed lateral sidesthereof. The superior pair of arms of a first X-shaped member can becoupled to an inferior pair of arms of a second X-shaped member. In oneembodiment, the at least two X-shaped members can be of a unitaryconstruction and can, for example, be formed from a polymeric material.In certain exemplary embodiments, the X-shaped members can have multipledurometers. In other embodiments, the multi-level spinal stabilizationsystem can include first and second connectors that are adapted tocouple the superior pair of arms of the first X-shaped member to theinferior pair of arms of the second X-shaped member. The first andsecond connectors can be, for example, first and second plates pivotallycoupled to one another. Each plate can be adapted to engage a terminalend of one arm of the superior and inferior pair of arms. In anotherembodiment, the first and second connectors can be in the form of aclamp mechanism that is adapted to engage a terminal end of one of thesuperior pair of arms and a terminal end of one of the inferior pair ofarms.

In yet another aspect, an exemplary method for stabilizing multipleadjacent vertebrae is provided and includes coupling an implant to aposterior portion of at least three adjacent vertebrae. The implant canhave a unitary configuration and it can be formed from an elastomericmaterial with multiple durometers to allow the implant to provideresistance to movement of the adjacent vertebrae.

In another exemplary embodiment, a method for stabilizing multipleadjacent vertebrae is provided and includes positioning a central spacerof a first X-shaped member between posterior elements of a firstvertebra and an adjacent second vertebra, coupling opposed superior armsof the first X-shaped member to the first vertebra, coupling opposedinferior arms of the first X-shaped member to the second vertebra,positioning a central spacer of a second X-shaped member betweenposterior elements of the second vertebra and an adjacent thirdvertebra, the second X-shaped member having opposed superior arms thatare coupled to the opposed inferior arms of the first X-shaped member,and coupling opposed inferior arms of the second X-shaped member to thethird vertebra.

In other aspects, a spinal stabilization device is provided having acentral spacer with opposed arms coupled to opposed lateral sidesthereof. Each arm can have a first portion that is adapted to couple toa first vertebra, and a second portion that is adapted to be positionedadjacent to a spinous process of a second adjacent vertebra such thatthe opposed arms are adapted to control or provide resistance tomovement, e.g., flexion, extension, lateral bending, and/or axialrotation, of first and second adjacent vertebrae. In one exemplaryembodiment, the second portion of the first arm can be coupled to thesecond portion of the second arm to form a U-shaped member that isadapted to be positioned around the spinous process of a second adjacentvertebra. The U-shaped member can be fixedly coupled to the centralspacer. The opposed arms can have a variety of other configurations. Forexample, they can be integrally formed with the central spacer. In otherembodiments the opposed arms can be substantially pliable, and caninclude, for example, a coil-shaped region.

In other aspects, a spinal stabilization device is provided having acentral spacer that is adapted to be positioned between posteriorelements of adjacent superior and inferior vertebrae. Opposed first andsecond arms can be coupled to opposed lateral sides of the centralspacer. Each arm can include a superior portion that extends in asuperior direction from the central spacer and that is adapted to becoupled to a superior vertebra. The superior portion of the first armand the superior portion of the second arm can diverge with respect toone another from the central spacer. Each arm can also include aninferior portion that extends in an inferior direction from the centralspacer. The inferior portion of each arm can extend substantiallyparallel to one another such that the inferior portion of the first armand the inferior portion of the second arm is adapted to engage aspinous process of an inferior vertebra therebetween to substantiallycontrol or provide resistance to movement, e.g., flexion, extension,lateral bending, and/or axial rotation, of adjacent superior andinferior vertebrae. In one exemplary embodiment, the superior portion ofeach of the first and second arms is curved. In another embodiment, theinferior portion of the first and second arms are coupled to one anotherto form a U-shaped member that is adapted to extend around a spinousprocess of an inferior vertebrae.

Exemplary methods for stabilizing adjacent vertebrae are also provided,and in one embodiment the method can include positioning a centralspacer between the posterior elements of first and second adjacentvertebrae. The central spacer can be adapted to substantially limitextension of the first and second adjacent vertebrae. The method canalso include positioning a first arm adjacent to a first lateral side ofthe central spacer such that a first portion of the first arm ispositioned adjacent to the first vertebra and a second portion of thefirst arm is positioned adjacent to the spinous process of the secondvertebra, and positioning a second arm adjacent to a second, opposedlateral side of the central spacer such that a first portion of thesecond arm is positioned adjacent to the first vertebra and a secondportion of the second arm is positioned adjacent to the spinous processof the second vertebra. The second portions of the first and second armscan substantially control or provide resistance to movement, e.g.,flexion, extension, lateral bending, and/or axial rotation of the firstand second adjacent vertebrae. In one exemplary embodiment, the secondportions of the first and second arms can be coupled to one another toform a substantially U-shaped member, and the U-shaped member can bearound the spinous process of the second vertebra. In another exemplaryembodiment, the first arm can be coupled to the first lateral side ofthe central spacer, and the second arm can be coupled to the second,opposed lateral side of the central spacer. The second portions of thefirst and second arms can engage opposed sides of the spinous process ofthe second vertebra.

Another exemplary method for stabilizing adjacent vertebrae can includepositioning a central spacer of a stabilization device between posteriorelements of adjacent vertebrae, and attaching arms extending fromopposed sides of the central spacer to at least one of the adjacentvertebrae. The stabilization device can be adapted to control or provideresistance to movement, e.g., flexion, extension, lateral bending,and/or axial rotation, of the adjacent vertebrae. In one exemplaryembodiment, attaching arms extending from opposed sides of the centralspacer to at least one of the adjacent vertebrae can include attaching afirst pair of arms extending from the central spacer to a superiorvertebra, and attaching a second pair of arms extending from the centralspacer to an inferior vertebra. The first and second pair of arms can bepivotally coupled to the central spacer to allow rotational movement ofthe central spacer between the posterior elements of the superior andinferior vertebrae. At least a portion of at least one of the first andsecond pairs of arms can be pliable to control or provide resistance tomovement, e.g., flexion, extension, lateral bending, and/or axialrotation, of the adjacent vertebrae. In another embodiment, attachingarms extending from opposed sides of the central spacer to at least oneof the adjacent vertebrae can include attaching a first portion of afirst arm to a first vertebra and attaching a first portion of a secondarm to the first vertebra. A second portion of each of the first andsecond arms can engage a spinous process of a second vertebra that isadjacent to the first vertebra.

In yet another exemplary embodiment, a method for stabilizing adjacentvertebrae is provided and includes determining a required amount ofspacing between posterior elements of adjacent vertebrae based on atension of a ligament extending between the posterior elements,positioning a central spacer having a height that corresponds to therequired amount of space determined between the posterior elements ofthe adjacent vertebrae, and attaching arms extending from opposed sidesof the central spacer to at least one of the adjacent vertebrae.

In another exemplary embodiment, a method for stabilizing adjacentvertebrae can include implanting a nucleus replacement between adjacentsuperior and inferior vertebrae, and coupling an implant to a posteriorportion of at least one of the superior and inferior vertebrae such thatthe implant is adapted to offload the nucleus replacement during axialrotation of the adjacent superior and inferior vertebrae.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1A is a perspective view of one exemplary embodiment of a spinalstabilization device having a unitary construction;

FIG. 1B is a posterior view of a portion of a human spinal column havingthe device shown in FIG. 1A implanted therein;

FIG. 2 is a posterior view of another exemplary embodiment of a spinalstabilization device having a central spacer with pliable arms coupledthereto;

FIG. 3 is a posterior view of a portion of a human spinal column showinga spinal stabilization device implanted therein and having a centralspacer with a first pair of arms coupled to a first lateral side thereofand a second pair of arms coupled to a second, opposed lateral sidethereof in accordance with another exemplary embodiment;

FIG. 4 is a posterior perspective view of a portion of a human spinalcolumn having an exemplary embodiment of a spinal stabilization deviceimplanted therein and having a central spacer with removable armscoupled thereto;

FIG. 5 is a posterior view of a portion of a human spinal column havinganother exemplary embodiment of a spinal stabilization device implantedtherein and having a central spacer with an arm slidably disposedtherethrough to form opposed first and second arms, and third and fourtharms coupled to the first and second arms;

FIG. 6A is a posterior view of a portion of a human spinal column havinga spinal stabilization device implanted therein and having a centralspacer adjustably coupled to opposed arms in accordance with yet anotherexemplary embodiment;

FIG. 6B is a perspective view of the opposed arms of the device shown inFIG. 6A;

FIG. 6C is a partially transparent side view of the cross-connector ofthe device shown in FIG. 6A;

FIG. 6D is a partially transparent side view of another embodiment of across-connector for use with the device shown in FIG. 6A;

FIG. 7 is a posterior view of yet another exemplary embodiment of aspinal stabilization device having opposed arms that are adapted toengage a spinous process;

FIG. 8 is a posterior view of another exemplary embodiment of asubstantially U-shaped spinal stabilization device having a U-shapedmember that is adapted to engage a spinous process;

FIG. 9 is a posterior view of yet another exemplary embodiment of amulti-level spinal stabilization device;

FIG. 10 is a top view of another exemplary of a connector for mating astabilization device to bone, showing the connector engaging two arms ofa spinal stabilization device;

FIG. 11A is a top view of a connector for mating two spinalstabilization devices to one another in accordance with anotherexemplary embodiment;

FIG. 11B is a posterior view of a portion of a human spinal columnshowing two stabilization devices implanted therein and connected toeach other with connectors as shown in FIG. 11A;

FIG. 12 is a side cross-sectional view of another exemplary embodimentof a connector for mating two spinal stabilization devices to oneanother;

FIG. 13 is a side cross-sectional view of yet another exemplaryembodiment of a connector for mating two spinal stabilization devices toone another;

FIG. 14 is a perspective view of one exemplary embodiment of a prior artpolyaxial bone screw for use with a spinal stabilization device of thepresent invention;

FIG. 15A is a posterior perspective view of one exemplary embodiment ofa connector for mating a spinal stabilization device to bone, showingtwo connectors mated to a terminal end of two of the arms of the deviceshown in FIG. 1A; and

FIG. 15B is a side cross-sectional view of one of the connectors shownin FIG. 15A.

DETAILED DESCRIPTION OF THE INVENTION

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the structure, function,manufacture, and use of the devices and methods disclosed herein. One ormore examples of these embodiments are illustrated in the accompanyingdrawings. Those skilled in the art will understand that the devices andmethods specifically described herein and illustrated in theaccompanying drawings are non-limiting exemplary embodiments and thatthe scope of the present invention is defined solely by the claims. Thefeatures illustrated or described in connection with one exemplaryembodiment may be combined with the features of other embodiments. Suchmodifications and variations are intended to be included within thescope of the present invention.

Various exemplary methods and devices are provided for stabilizing theposterior elements of the spine, and more preferably methods and devicesare provided for sharing the load with the intervertebral disc, thefacet joints, the ligaments, and the muscles of the spinal column. Themethods and devices can also stabilize and protect the facet joints inthe lumbar spine, as well as other posterior spinal muscles andligaments. The methods are devices can be used with the natural disc orwith an artificial disc replacement. In certain exemplary embodiments,the methods and devices can be adapted to substantially control orprovide resistance to movement of at least two adjacent vertebrae. Themovement can include any one or a combination of flexion, extension,lateral bending, and/or axial rotation or at least two adjacentvertebrae. The methods and devices can also be adapted for minimallyinvasive use. A person skilled in the art will appreciate that theparticular devices and methods disclosed herein can be used for avariety of other medical purposes.

FIG. 1A illustrates one exemplary embodiment of a spinal stabilizationdevice 10. As shown, the device 10 is substantially X-shaped and is of aunitary construction. In particular, the exemplary device 10 includes acentral spacer 12 that is adapted to be disposed between posteriorelements of two adjacent vertebrae, and two pairs of arms 14 a, 14 b, 16a, 16 b that extend from each lateral side 12 a, 12 b of the centralspacer 12, such that the device 10 has a total of four arms 14 a, 14 b,16 a, 16 b. Two of the arms, i.e., the superior arms 14 a, 16 a, extendin a superior direction from the central spacer 12 to couple to avertebra that is positioned superior to the central spacer 12. The othertwo arms, i.e., the inferior arms 14 b, 16 b, can extend laterallyoutward, or they can extend in an inferior direction, from the centralspacer 12 to couple to a vertebra that is inferior to the central spacer12.

The central spacer 12 can have variety of configurations, but in oneexemplary embodiment, the central spacer 12 has a shape and size thatallows the central spacer 12 to be positioned between two posteriorelements, such as the spinous processes, of two adjacent vertebrae andthat is adapted to limit or prevent extension of the adjacent vertebrae.As shown in FIG. 1A, the exemplary central spacer 12 is substantiallywedge-shaped and has an anterior portion 12 c that is substantiallysquare or rectangular in shape, and a posterior portion 12 d that has aheight h that tapers or decreases in a posterior direction to form awedge. Such a configuration allows the central spacer 12 to bepositioned between two spinous processes of two adjacent vertebrae andto substantially limit of prevent extension of the vertebrae relative toone another. The central spacer 12 can have a variety of other shapesand sizes including, by way of non-limiting example, a round, oval,elliptical, or rectangular shape. A person skilled in the art willappreciate that while the central spacer 12 is described as beingadapted to be positioned between the spinous processes of adjacentvertebrae, that the spinous processes of the adjacent vertebrae do notnecessarily need to be present, as they may be removed in a laminectomyprocedure. Accordingly, the central spacer 12 can be positioned betweenother posterior elements of the adjacent vertebrae, or it can bepositioned in the general vicinity of the removed spinous processes.

The central spacer 12 can also be formed from a rigid material, or itcan be formed from a semi-rigid, pliable or compressible material toallow some compression of the central spacer 12 to occur upon extensionof the adjacent vertebrae. A person having ordinary skill in the artwill appreciate that the material used to form the central spacer 12 canbe selected based on the intended use. For example, a material can beselected based on the patient's size and condition to have a particularstiffness, deformability, or compressibility which corresponds to adesired degree of extension intended. The particular properties of thecentral spacer 12 can also vary throughout the central spacer 12, andthe central spacer 12 can be uniform or non-uniform throughout the bodythereof. In an exemplary embodiment, the central spacer 12 is formedfrom a polymer, and more preferably a biocompatible polymer, such aspolyurethane, composite reinforced polyurethane, silicone, etc.

The arms 14 a, 14 b, 16 a, 16 b that extend from the central spacer 12can also have a variety of configurations, shapes, and sizes, and theconfiguration of each arm 14 a, 14 b, 16 a, 16 b can vary depending onthe particular procedure being performed and the desired implantlocation. In general, the arms 14 a, 14 b, 16 a, 16 b are preferablyrod-shaped members having a substantially elongate shape. While the arms14 a, 14 b, 16 a, 16 b can extend from any portion of the central spacer12, in the exemplary embodiment shown in FIG. 1A, the superior arms 16a, 16 b extend from opposed superior ends of the lateral sides 12 a, 12b of the anterior portion 12 c of the central spacer 12. The superiorarms 16 a, 16 b can diverge with respect to one another away from thecentral spacer 12, and each arm 16 a, 16 b can have a substantiallycurved configuration. Such a shape allows the superior arms 16 a, 16 bto mate to the pedicles of a vertebra positioned superior to the device10. The inferior arms 14 b, 16 b can also extend from opposed lateralsides 12 a, 12 b of the central spacer 12, however in the illustratedexemplary embodiment they extend from an inferior end of the anteriorportion 12 c of the central spacer 12. The inferior arms 14 b, 16 b canextend laterally such that they are substantially co-axial with oneanother, or they can extend in an inferior direction with respect to thecentral spacer 12. The laterally-extending arms 14 b, 16 b shown in FIG.1B allow the arms 14 b, 16 b to mate to the pedicles of a vertebrapositioned inferior to the central spacer 12. Again, a person skilled inthe art will appreciate that the shape, size, and configuration of thearms 14 a, 14 b, 16 a, 16 b can vary depending on the intended use andimplant location.

Each arm 14 a, 14 b, 16 a, 16 b can also be substantially pliable tocontrol or provide resistance to movement, e.g., flexion, extension,lateral bending, and/or axial rotation, of the adjacent vertebraecoupled thereto. The amount of pliability, e.g., flexibility and/orelasticity, of each arm 14 a, 14 b, 16 a, 16 b can vary depending on theproperties of the material used to form the device 10, and a materialcan be selected to achieve a desired result. The pliability can alsovary along the length of each arm 14 a, 14 b, 16 a, 16 b. For example,the arms 14 a, 14 b, 16 a, 16 b can be more pliable adjacent to thecentral spacer 12, and can be more rigid adjacent to the terminal endthereof. Rigid terminals ends are particularly advantageous tofacilitate mating of the device 10 to adjacent vertebrae. Otherexemplary techniques for providing rigid terminal ends include, by wayof non-limiting example, metal sleeves that slide over the ends of thearms 14 a, 14 b, 16 a, 16 b and that can be crimped to engage the arms14 a, 14 b, 16 a, 16 b and prevent the sleeves from sliding off.Alternatively, a metal over-mold or a hard polymer over-mold can beprovided on the ends of the arms 14 a, 14 b, 16 a, 16 b.

In one exemplary embodiment, the device 10 has a unitary configurationand is formed from an elastomer with multiple durometers, i.e., varyingdegrees of surface resistivity or material hardness throughout thedevice 10. For example, the central spacer 12 can have an intermediatedurometer, the portion of the arms 14 a, 14 b, 16 a, 16 b adjacent tothe central spacer 12 can have a low durometer, and the terminal ends ofthe arms 14 a, 14 b, 16 a, 16 b can have a high durometer such that theyare extremely rigid for interfacing with fastening elements to mate thearms 14 a, 14 b, 16 a, 16 b to adjacent vertebrae.

FIG. 1B illustrates spinal stabilization device 10 in use. As shown, thecentral spacer 12 is positioned between two spinous processes S_(s),S_(i) of two adjacent vertebrae, i.e., a superior vertebra V_(s) and aninferior vertebra V_(i). Where the device 10 is formed from a pliablematerial, the spacer 12 can be positioned between the spinous processesS_(s), S_(i) by squeezing two of the arms, e.g., arms 14 a, 14 btogether and passing the arms 14 a, 14 b between the spinous processesS_(s), S_(i). This will avoid the need to sacrifice the supraspinousligament that connects the spinous processes S_(s), S_(i). Once thespacer 12 is positioned between the spinous processes S_(s), S_(i) ofthe adjacent vertebrae V_(s), V_(i), the tension of the ligament canoptionally be used to determine whether the spacer 12 has theappropriate size or height. If the spacer 12 is too small or too large,the device 10 can be removed and replaced with another device 10 havingan appropriately sized spacer 12.

As is further shown in FIG. 1B, when the central spacer 12 is positionedbetween the spinous processes S_(s), S_(i), the superior arms 14 a, 16 aextend toward the pedicles P_(s1), P_(s2) of the superior vertebraV_(s), and the inferior arms 14 b, 16 b extend toward the pediclesP_(i1), P_(i2) of the inferior vertebra V_(i). While not shown, one ormore bone-engaging devices, such as a mono-axial or poly-axial bonescrew can be used to mate the arms 14 a, 14 b, 16 a, 16 b to thepedicles P_(s1), P_(s2), P_(i1), P_(i2). Alternatively, a mobilepoly-axial screw can be used. Exemplary mobile poly-axial screws aredescribed in U.S. Publication No. 2004/0225289 of Biedermann et al., andWO 2005/044123 of Biedermann et al., which are hereby incorporated byreference in their entirety. The central spacer 12 can at leastpartially rotate to facilitate mating of the arms 14 a, 14 b, 16 a, 16 bto the pedicles P_(s1), P_(s2), P_(i1), P_(i2). While four arms 14 a, 14b, 16 a, 16 b are provided, it is not necessary to mate all four arms 14a, 14 b, 16 a, 16 b to the adjacent vertebrae V_(s), V_(i). Only two ofthe four arms 14 a, 14 b, 16 a, 16 b can be mated to the vertebraeV_(s), V_(i). One exemplary embodiment of a prior art polyaxial bonescrew will be discussed in more detail below with respect to FIG. 14. Aperson skilled in the art will appreciate that virtually any techniqueknown in the art for mating a rod to bone can be used to implant thevarious exemplary spinal stabilization devices disclosed herein. Onceimplanted 10, the central spacer 12 can function to limit or stopextension of the adjacent vertebrae V_(s), V_(i), and the arms 14 a, 14b, 16 a, 16 b can control or provide resistance to movement, e.g.,flexion, extension, lateral bending, and/or axial rotation of theadjacent vertebrae V_(s), V_(i). The device 10 can also be effective toprovide stability to the facet joints, which may or may not be removed,and to other posterior elements, such as the natural disc, a nucleusreplacement, or a disc replacement. The device 10 is particularlyadvantageous for use with nucleus replacements, as the device 10 canoffload the nucleus replacement during axial rotation of the adjacentvertebrae.

FIG. 2 illustrates another exemplary embodiment of a spinalstabilization device 20. The device 20 is very similar to device 10shown in FIGS. 1A and 1B, however device 20 is not of a unitaryconstruction, but rather the arms 24 a, 24 b, 26 a, 26 b are fixedlymated to the central spacer 22. The arms 24 a, 24 b, 26 a, 26 b can bemated to the central spacer 22 using a variety of techniques, however inthe embodiment shown in FIG. 2 the central spacer 22 is formed from apolymeric material and the arms 24 a, 24 b, 26 a, 26 b are adheredthereto using an adhesive or an overmold. The arms 24 a, 24 b, 26 a, 26b also include a pliable region formed thereon to provide pliability,e.g., flexibility and/or elasticity, to a portion of the arms 24 a, 24b, 26 a, 26 b. In particular, each arm 24 a, 24 b, 26 a, 26 b is in theform of a spring rod having a coiled region 24 c, 24 d, 26 c, 26 dformed thereon, preferably on a first portion 24 a ₁, 24 b ₁, 26 a ₁, 26b of each arm 24 a, 24 b, 26 a, 26 b. The coiled region 24 c, 24 d, 26c, 26 d can be formed from a coiled cut-out formed in the arms 24 a, 42b, 26 a, 26 b to allow the arms 24 a, 24 b, 26 a, 26 b to flex. Byproviding the coiled region 24 c, 24 d, 26 c, 26 d in the first portion24 a ₁, 24 b ₁, 26 a ₁, 26 b ₁ of each arm 24 a, 24 b, 26 a, 26 b, asecond or terminal portion 24 a ₂, 24 b ₂, 26 a ₂, 26 b ₂ of each arm 24a, 24 b, 26 a, 26 b can be substantially rigid to facilitate mating ofthe device 20 to bone. A person skilled in the art will appreciate thatthe arms 24 a, 24 b, 26 a, 26 b can be formed from a variety ofmaterials, but in one exemplary embodiment the arms 24 a, 24 b, 26 a, 26b are formed from a metal, such as a titanium alloy, stainless steel, ora shape-memory material.

While FIGS. 1A-2 illustrate various embodiments of spinal stabilizationdevices 10, 20 that have arms integrally formed with or fixedly mated tothe central spacer, the arms can optionally be removably matable to thecentral spacer. Removable arms can be advantageous as they will allowthe spacer to be positioned between the spinous processes or otherposterior elements without sacrificing the ligament. The arms can thenbe attached to the central spacer and mated to the bone to stabilize thevertebrae. While various techniques can be used to provide removablearms, FIG. 3 illustrates one exemplary embodiment of a spinalstabilization device 30 having removable arms. As shown, the deviceincludes a central spacer 32, a first pair of arms 34 a, 34 b coupled toa first lateral side 32 a of the central spacer 32, and a second pair ofarms 36 a, 36 b coupled to a second, opposed lateral side 32 b of thecentral spacer 32. The first pair of arms 34 a, 34 b can be coupled toor integrally formed with one another, and the second pair of arms 36 a,36 b can likewise be coupled to or integrally formed with one another,as shown. The first pair of arms 34 a, 34 b can removably mate to thefirst lateral side 32 a of the central spacer 32 and the second pair ofarms 36 a, 36 b can removably mate to the second lateral side 32 b ofthe central spacer 32, or alternatively the first and second pair ofarms 34 a, 34 b, 36 a, 36 b can mate to one another through a boreformed in the central spacer 32. A fastening element such as a setscrew, pin, locking nut, rivet, etc., can be used to mate the arms 34 a,34 b, 36 a, 36 b to the central spacer 32 and/or one another. A personskilled in the art will appreciate that virtually any fasteningmechanism can be used to mate the pairs of arms 34 a, 34 b, 36 a, 36 bto the central spacer 32.

Each arm 34 a, 34 b, 36 a, 36 b can also be pliable to control orprovide resistance to movement, e.g., flexion, extension, lateralbending, and/or axial rotation of the adjacent vertebrae coupledthereto. While various techniques can be used to provide pliability,including those previously discussed herein, in one exemplary embodimenteach arm 34 a, 34 b, 36 a, 36 b can include a first portion 34 a ₁, 34 b₁, 36 a ₁, 36 b ₁ adjacent to the central spacer 32 that is formed forma thin pliable material, and a second or terminal portion 34 a ₂, 34 b₂, 36 a ₂, 36 b ₂ that is formed from a more rigid material to allow thearms 34 a, 34 b, 36 a, 36 b to be mated to bone.

In use, the configuration shown in FIG. 3 allows the central spacer 32to be positioned prior to attaching the arms 34 a, 34 b, 36 a, 36 bthereto, thereby allowing the ligament extending between the spinousprocesses S_(s), S_(i) of the adjacent vertebrae V_(s), V_(i) tomaintain in tact. The configuration can also allow the arms 34 a, 34 b,36 a, 36 b to rotate relative to the central spacer 32 prior to lockingthe arms 34 a, 34 b, 36 a, 36 b thereto, thus allowing the arms 34 a, 34b, 36 a, 36 b to be positioned at desired. Furthermore, although notshown in detail, the attachment to the central spacer 32 can be doneusing hemispherical mating surfaces to allow pivotal adjustment of thearms 34 a, 34 b, 36 a, 36 b relative to the spacer 32. Such anadjustment mechanism allows accurate placement of the spacer 32 for avariety of anatomies without putting excessive loading on the arms 34 a,34 b, 36 a, 36 b. After locating the spacer 32 and the arms 34 a, 34 b,36 a, 36 b, all units can be combined using any of a variety of lockingmechanisms, including screws, rivets, pins, adhesives, etc.

FIG. 4 illustrates another exemplary embodiment of a spinalstabilization device 40 having removable arms 44 a, 44 b, 46 a, 46 b. Asshown, the device 40 includes a central spacer 42 that is adapted to bepositioned between spinous processes S_(s), S_(i) of adjacent superiorand inferior vertebra V_(s), V_(i), and four arms 44 a, 44 b, 46 a, 46 bthat are removably mated to the central spacer 42. The arms 44 a, 44 b,46 a, 46 b can have a variety of configurations, but in the illustratedembodiment they are very similar to the spring rod arms 24 a, 24 b, 26a, 26 b of the device 20 shown in FIG. 2. Accordingly, the arms 44 a, 44b, 46 a, 46 b will not be described in detail.

The central spacer 42 can have virtually any shape and size, but in theillustrated embodiment it has a generally elongate shape with a heightat a mid-portion that is less than a height of the central spacer 42 atthe opposed lateral sides thereof. Each lateral side 42 a, 42 b can bein the form of a clamp to receive the arms 44 a, 44 b, 46 a, 46 btherein. For example, the lateral sides 42 a, 42 b can include asuperior opening and an inferior opening formed therein. FIG. 4 onlyillustrates the superior and inferior openings 43 _(s), 43 _(i) inlateral side 42 b. Each opening 43 _(s), 43 _(i) has a shape and sizethat allows one end of one of the arms 44 a, 44 b, 46 a, 46 b to be slidtherein. A locking mechanism can then be used to cause the centralspacer 42 to clamp down onto and engage the arms 44 a, 44 b, 46 a, 46 b.While the locking mechanism can have a variety of configurations, in theillustrated embodiment the locking mechanisms are in the form of setscrews 47 a, 47 b that extend through threaded bores formed in theposterior and anterior faces of the central spacer 42 to pull theposterior and anterior faces toward one another, thereby causing thecentral spacer 42 to engage the arms 44 a, 44 b, 46 a, 46 b.

In use, the central spacer 42 is preferably passed between the spinousprocesses S_(s), S_(i) of the adjacent vertebrae V_(s), V_(i), and thearms 44 a, 44 b, 46 a, 46 b can then be slid into the correspondingopenings in the central spacer 42. The locking mechanisms 47 a, 47 b canbe pre-disposed within the central spacer 42, or they can be insertedinto the central spacer 42 after the arms 44 a, 44 b, 46 a, 46 b aredisposed therein. The locking mechanisms 47 a, 47 b can be tightened toengage the arms 44 a, 44 b, 46 a, 46 b, preventing removably thereoffrom the central spacer 42. At least two of the arms, and preferably arefour of the arms 44 a, 44 b, 46 a, 46 b, can then be mated to thesuperior and inferior vertebrae V_(s), V_(i) to provide stability to theposterior elements of the spine. In this embodiment, the central spacer42 is preferably formed from a rigid material, such as a metal, and thusthe central spacer 42 can function as a hard stop to prevent extensionof the vertebrae V_(s), V_(i). The spring rod arms 44 a, 44 b, 46 a, 46b will control or provide resistance to movement, e.g., flexion,extension, lateral bending, and/or axial rotation, of the vertebraeV_(s), V_(i). A person skilled in the art will appreciate that a varietyof other techniques can be used to provide arms that removably mate to acentral spacer.

FIG. 5 illustrates another exemplary embodiment of a spinalstabilization device 50. In this embodiment, the device 50 includes acentral spacer 52 with an elongate arm 56 that is slidably disposedthrough a laterally-extending lumen formed in the central spacer 52. Asa result, the elongate arm 56 forms opposed first and second arms 56 a,56 b extending from opposed lateral sides of the central spacer 52. Thedevice 50 also include a third arm 54 a that is removably attached tothe first arm 56 a, and a fourth arm 54 b that is removably attached tothe second arm 56 b. Such a configuration will allow the central spacer52 with arm 56 disposed therethrough to be inserted between the spinousprocesses S_(s), S_(i) of adjacent superior and inferior vertebraeV_(s), V_(i), and then the third and fourth arms 54 a, 54 b can be matedthereto.

The central spacer 52 and the elongate arm 56 can have a variety ofconfigurations, but as shown the central spacer 52 is substantiallytubular in shape and the elongate arm 56 is in the form of an elongaterod that extends through the central spacer 52. The elongate arm 56 canbe curved to facilitate mating thereof to the pedicles P_(i1), P_(i2) ofthe inferior vertebra V_(i), as shown, or they can have a shape tofacilitate mating thereof to the pedicles P_(s1), P_(s2) of the superiorvertebra V_(s).

The third and fourth removable arms 54 a, 54 b can also have a varietyof configurations, but in the illustrated exemplary embodiment they arecoiled to provide pliability, and they are adapted to mate to the firstand second arms 56 a, 56 b. In particular, the third and fourth arms 54a, 54 b each include a spherical head 55 a, 55 b formed on one endthereof for seating a portion of the elongate arm 56 therein. Thespherical head 55 a, 55 b is adapted to receive a locking mechanism suchas a set screw 57 a, 57 b, therein for locking the third and fourth arms54 a, 54 b to the first and second arms 56 a, 56 b. The third and fourtharms 54 a, 54 b can also include a hollow coiled portion extending fromthe spherical head 55 a, 55 b for providing pliability to the arms 54 a,54 b to allow flexion of the adjacent vertebrae V_(s), V_(i). The thirdand fourth arms 54 a, 54 b can, however, have a variety of otherconfigurations and they can be formed from a pliable and/or rigidmaterial. As is further shown in FIG. 5, a terminal end 54 _(t1), 54_(t2) of the third and fourth arms 54 a, 54 b can be in the form of rodsthat are adapted to be received within a bone-engaging device, such as apolyaxial bone screw as will be discussed in more detail below. A personskilled in the art will appreciate that a variety of other techniquescan be used to removably mate one or more arms to the elongate arm 56.

In use, as indicated above, the central spacer 52, with or without theelongate arm 56 disposed therethrough, is preferably positioned betweenthe spinous processes S_(s), S_(i). In an exemplary embodiment, theelongate arm 56 is preferably pre-disposed within the central spacer 52,and the central spacer 52 is configured to provide a snug fit with theelongate arm 56 to prevent sliding of the arm 56 with respect to thespacer 52. Once the spacer 52 and arm 56 are properly positioned, thethird and fourth arms 54 a, 54 b can be coupled to the first and secondarms 56 a, 56 b. Preferably at least two of the arms 54 a, 54 b, 56 a,56 b are also coupled to the pedicles P_(s1), P_(s2), P_(i1), P_(i2) ofthe vertebrae V_(s), V_(i).

In other embodiments, the spinal stabilization device can have a centralspacer that is adjustably matable to opposed arms to allow the centralspacer to be positioned as desired. FIG. 6A illustrates one suchexemplary embodiment. As shown, the spinal stabilization device 60generally includes a central spacer 62 with a cross-connector 68 coupledthereto, and opposed arms 64, 66 that are matable to the cross-connector68. In particular, the central spacer 62, which can have any shapeincluding square, cylindrical, or rectangular, has a central lumenformed therein and extending between opposed lateral sides thereof. Thecross-connector 68 can be in the form of a clamp that is adapted toextend through the central lumen formed in the central spacer 62. Asshown in detail in FIG. 6C, the cross-connector 68 includes two members69 a, 69 b that define two openings 68 o ₁, 68 o ₂ formed therebetweenfor receiving the arms 64, 66 of the device 60. A fastening element,such as a set screw 68 s, can be inserted through a central bore 68 cformed in the cross-connector 68 to engage the arms 64, 66 within theopenings 68 o ₁, 68 o ₂. A person skilled in the art will appreciatethat the cross-connector 68 can have a variety of other configurations,and that a variety of other techniques can be used to mate the arms 64,66 to the central spacer 62. By way of non-limiting example, FIG. 6Dillustrates another embodiment of a cross-connector 68′ for use with thedevice 60 shown in FIG. 6A. In this embodiment, the cross-connector 68′has hook-shaped ends 68 a′, 68 b′, rather than openings formedtherethrough, for seating the arms 64, 66 of the device 60. A lockingmechanism 68 s′ can be inserted through a central bore 68 c′ to causeopposed engagement mechanisms 69 a′, 69 b′ to slide outward and engagethe arms 64, 66.

The arms 64, 66 of the device 60 can also have a variety ofconfigurations, but in an exemplary embodiment they are substantiallysimilar to the arms 34 a, 34 b, 36 a, 36 b shown in FIG. 3. In thisembodiment, however, each arm 64, 66 is substantially planar except forsuperior and inferior terminal end portions 64 a, 64 b, 66 a, 66 b and acentral portion 64 c, 66 c of each arm 64, 66. The superior and inferiorterminal end portions 64 a, 64 b, 66 a, 66 b and the central portion 64c, 66 c can have a substantially cylindrical shape to allow the arms 64,66 to mate to adjacent vertebrae, and to allow the central portions 64c, 66 c to fit within the opening 68 o ₁, 68 o ₂ in the cross-connector68. A person skilled in the art will appreciate that each arm 64, 66 canbe cylindrical along the entire length thereof, or that the arms 64, 66can have a variety of other shapes.

In use, when the arms 64, 66 are mated to adjacent superior and inferiorvertebrae V_(s), V_(i), as shown in FIG. 6A, the central spacer 62 andcross-connector 68 can be moved proximally and distally, as well as inan anterior and posterior direction, relative to the adjacent vertebraeV_(s), V_(i) to position the central spacer 62 as desired. The angle ofthe arms 64, 66 relative to the adjacent vertebrae V_(s), V_(i) can alsobe adjusted using polyaxial bone screws, mobile bone screws, or screwsthat lock, to connect the arms to the adjacent vertebrae V_(s), V_(i),as will be discussed in more detail with respect to FIG. 9. Once thecentral spacer 62 and the cross-connector 68 are in a desired position,a locking mechanism, such as a set screw 68 s, can be inserted through acentral bore formed in the central spacer 62 and through the centralbore 68 c formed in the cross-connector 68 to cause the cross-connector68 to clamp onto and engage the arms 64, 66. As a result, the centralspacer 62 can be maintained in a substantially fixed position relativeto the arms 64, 66. A person skilled in the art will appreciate that thearms 64, 66, the central spacer 62, and the cross-connector 68 can havea variety of other configurations, including various otherconfigurations disclosed herein. The arms 64, 66, the central spacer 62,and the cross-connector 68 can also be formed from a variety ofmaterials, including polymeric materials, metallic materials, andcombinations thereof, and the materials can be pliable or rigid, orcombinations thereof.

In other exemplary embodiments, the spinal stabilization device can beadapted to engage at least one spinous process to control or provideresistance to movement, e.g., flexion, extension, lateral bending,and/or axial rotation, of adjacent vertebrae. FIG. 7 illustrates oneexemplary embodiment of such a spinal stabilization device 70. As shown,the device 70 is substantially Y-shaped and includes a central spacer 72with a first arm 74 coupled to a first lateral side thereof, and asecond arm 76 coupled to a second lateral side thereof. The arms 74, 76can be fixedly mated to, removably mated to, or of unitary constructionwith the central spacer 72. For example, each arm 74, 76 can be adaptedto receive a fastening element, such as a set screw, therethrough formating each arm 74, 76 to the central spacer 72. Each arm 74, 76 canalso include a first portion, e.g., a superior portion 74 a, 76 a thatis adapted to mate to a superior vertebra V_(s), and a second portion,e.g., an inferior portion 74 b, 76 b that is adapted to be positionedadjacent to the spinous process S_(i) of an inferior vertebra V_(i). Thefirst portion 74 a, 76 a of each arm 74, 76 can have a variety of shapesand sizes to facilitate mating to the superior vertebra V_(s), but inthe illustrated exemplary embodiment the superior portion 74 a, 76 a ofeach arm 74, 76 is substantially curved such that the arms 74, 76diverge with respect to one another away from the central spacer 72. Thearms 74, 76 can also be formed from a variety of materials, includingpliable materials to allow the arms to be positioned as desired duringimplantation. Where the device 70 only attaches to the vertebrae by thearms 74, 76, the arms can optionally be rigid, as the inferior portion74 b, 76 b of the arms 74, 76 will allow controlled movement of theadjacent vertebrae.

The inferior portion 74 b, 76 b of each arm 74, 76 can also have avariety of shapes and sizes, but in an exemplary embodiment the inferiorportions 74 b, 76 b are adapted to engage the inferior spinous processS_(i) therebetween, preferably at the base thereof, to substantiallycontrol or provide resistance to movement, e.g., flexion, extension,lateral bending, and/or axial rotation, of the adjacent vertebrae V_(s),V_(i). By way of non-limiting example, the inferior portions 74 b, 76 bcan be substantially elongate, flat members that grip the spinousprocess S_(i), or they can be rod-shaped and can include protectivecovers disposed there over or features formed thereon to facilitategripping of the spinous process Si. The inferior portions 74 b, 76 b canalso be pliable to provide some resistance to flexion, extension,lateral bending. and/or axial rotation. The inferior portions 74 b, 76 bcan also be adapted to contact the lamina of the inferior vertebra V_(i)to further aid in limiting extension, axial rotation, and/or lateralbending of the adjacent vertebrae. For example, the distal-most orterminal end of the inferior portions 74 b, 76 b can each have a shape,e.g., flat, rounded, spherical, etc., that is adapted to abut againstthe lamina of the inferior vertebra V_(i), and the shape and size can beconfigured to maximize the contact area between the inferior portions 74b, 76 b and the inferior vertebra V_(i).

In another embodiment, the stabilization device can engage the spinousprocess to further control or provide resistance to movement of theadjacent vertebrae. FIG. 8 illustrates one exemplary embodiment of sucha stabilization device 80. As shown, the device 80 is similar to device70, except that the inferior portions of the arms 84, 86 are coupled toone another to form a U-shaped member 88. The U-shaped member 88 canhave a variety of configurations and it can be integrally formed withthe device 80, or it can be separate from the device 80 to allow it tobe coupled to the device 80 either prior to or after implantation. Wherethe device 80 has a multi-component configuration, by way ofnon-limiting example the U-shaped member 88 can be formed from a band orcord that can function as an artificial ligament. Such a configurationallows the U-shaped member 88 to be attached to the device 80 afterimplantation thereby avoiding the need to cut the supraspinous ligament.In particular, the U-shaped member 88 can be inserted between theinterspinous space without disrupting the ligament, and it can then beattached to the device 80.

In use, the central spacer 82 is positioned between adjacent spinousprocesses, the opposed superior arms 84, 86 are mated to a superiorvertebra, and the U-shaped member 88 is positioned around the spinousprocess to engage the spinous process and thereby control or provideresistance to axial rotation, lateral bending, flexion, and/orextension. For example, during flexion the spinous processes of theadjacent vertebrae will move away from one another. As a result, theU-shaped member 88 will stretch thereby providing resistance to flexion.

A person skilled in the art will appreciate that devices 70 and 80,while shown being adapted to engage a spinous process of an inferiorvertebra, can be reversed such that the arms 74, 76, 84, 86 mate to aninferior vertebra, and the device 70, 80 engages a spinous process of asuperior vertebra. A person skilled in the art will also appreciate thatthe devices 70, 80 shown in FIGS. 7 and 8, as well as the various otherexemplary spinal fixation devices disclosed herein, can be formed fromunitary components, or components that are fixedly or removably mated tothe central spacer. The various devices can also include any combinationof features disclosed herein and a variety of other features known inthe art.

Various exemplary multi-level spinal stabilization devices are alsoprovided. FIG. 9 illustrates one exemplary embodiment of a multi-levelspinal stabilization device 30. In this embodiment, the device 90 isvery similar to device 10 shown in FIGS. 1A and 1B. In particular, thedevice 90 is formed from three x-shaped bodies 90 a, 90 b, 90 c, eachsimilar to device 10, that are mated to one another. Each body 90 a, 90b, 90 c has a central spacer 92, 92′, 92″ with a pair of superior arms94 a, 96 a, 94 a′, 96 a′, 94 a″, 96 a″, and a pair of inferior arms 94b, 96 b, 94 b′, 96 b′, 94 b″, 96 b″. The inferior arms 94 b, 96 b of thefirst body 90 a are mated to the superior arms 94 a′, 96 a′ of thesecond body 90 b, and the inferior arms 94 b′, 96 b′ of the second body90 b are mated to the superior arms 94 a″, 96 a″ of the third body 90 c.The arms of the bodies 90 a, 90 b, 90 c can be mated to each other usinga variety of techniques, and they can be fixedly mated, removably mated,or unitarily or integrally formed with one another. In the embodimentshown in FIG. 9, the device 90 is formed of a unitary construction, suchthat the entire device 90 is molded to create a composite device. Inuse, the device 90 can be implanted by positioning the central spacer92, 92′, 92″ of each body 90 a, 90 b, 90 c between spinous processes orother posterior elements of adjacent vertebrae, and connecting thesuperior arms 94 a, 94 b of the first body 90 a to the superior-mostvertebra, and attaching the inferior arms 94 b″, 96 b″ of the third body90 b to the inferior-most vertebra being stabilized. The device 90 canthus function as previously described with respect to FIG. 1A tosubstantially control or provide resistance to movement, e.g., flexion,extension, lateral bending, and/or axial rotation. The degree to whichextension, flexion, lateral bending, and/or axial rotation arecontrolled can, of course, vary depending on the particularconfiguration and properties of the device. For example, the material(s)used to form the device 90 can be selected to obtain a desired result. Aperson having ordinary skill in the art will appreciate that, while onlythree bodies 90 a, 90 b, 90 c are shown, the device 90 can include anynumber of bodies based on the desired level of vertebrae beingstabilized.

A multi-level spinal stabilization device can also be provided by matingthe arms of one spinal stabilization device to the arms of anotherspinal stabilization device. While various techniques can be used tomate the arms, in one exemplary embodiment a connector can be used. FIG.10 illustrates one embodiment of a connector 100 that is in the form ofa clamp. The illustrated clamp connector 100 is substantially V-shapedor triangular, and it can include two openings (not shown) formedtherein for receiving the terminal ends of two arms. A fasteningelement, such as a set screw 102, can extend through the connector 100to clamp down on and engage the arms within the connector 100. Theconnector 100 can also include a bone screw 104 mated thereto to allowthe connector 100 to be mated to bone. The bone screw 104 can optionallybe polyaxial relative to the connector 100. In other exemplaryembodiments, the connector 100 can be modular to allow the two armsmated thereto to be angular adjusted relative to one another. A personskilled in the art will appreciate that a variety of other techniquescan be used to mate the arms to one another.

FIG. 11A illustrated another exemplary embodiment of a connector 110 formating the arms of two spinal stabilization devices. In this embodimentthe connector 110 includes two plate-like members 112, 114 that arepivotally mated to one another using, for example, a fastening element116, such as a bolt and nut. The terminal end of each plate 112, 114 canbe adapted to engage an arm of a spinal stabilization device. This canbe achieved using a variety of techniques including, for example, aclamping mechanism, a polyaxial connection, etc., exemplary embodimentsof which will be described below with respect to FIGS. 12 and 13. FIG.11B illustrates connector 110 in use, showing two spinal stabilizationdevices D₁, D₂ having arms connected by two connectors 110, 110′.

FIGS. 12 and 13 illustrate exemplary embodiments of techniques forconnecting the terminal end of each plate 112, 114 to an arm of a spinalstabilization device. In the embodiment shown in FIG. 12, the connector120 is a clamp having a first end 122 that is adapted to clamp andengage an arm of a stabilization device, and a second end 124 that isadapted to receive a spherical member. The spherical member can beformed on the plate-like member 112, 114 shown in FIGS. 11A and 11B. Asingle fastening element 126 can be used to close the clamp connector120. In the embodiment shown in FIG. 13, the connector 130 is similarlyin the form of a clamp having a fastening element 136 that is adapted tobe disposed therethrough to clamp onto an arm of a spinal stabilizationdevice.

As previously indicated, when a spinal stabilization device isimplanted, preferably one or more of the arms of the device is mated toa vertebra. While a variety of bone-engaging devices can be used to matethe arm(s) to a vertebra, in one exemplary embodiment a polyaxial bonescrew is used. FIG. 14 illustrates one exemplary embodiment of a priorart polyaxial bone screw 140 for use in connecting an arm of astabilization device to bone, and more preferably to the pedicle of avertebra. The bone screw 140 can be implanted in the pedicle, and an armof a device can be positioned within a receiving recess 142 formed inthe head 144 of the bone screw 140. A fastening element, such as alocking nut, can then be threaded onto the head 144 of the bone screw140 to engage the arm. A person skilled in the art will appreciate thata variety of other techniques known in the art can be used to mate thestabilization devices to bone, and FIG. 14 merely illustrates oneexemplary embodiment of one such device.

FIGS. 15A and 15B illustrate another exemplary embodiment of a devicefor mating an arm to bone. In this embodiment, the bone-engaging element150 is in the form of a clamp have a first end 152 with a cylindricalrecess formed therein for receiving a terminal end of an arm A_(t), anda second end 154 having a spherical recess for receiving a sphericalhead 156 a of a bone screw 156. Such a configuration allows the bonescrew 156 to be positioned at a desired angle relative to the arm A_(t).

One of ordinary skill in the art will appreciate further features andadvantages of the invention based on the above-described embodiments.Accordingly, the invention is not to be limited by what has beenparticularly shown and described, except as indicated by the appendedclaims. All publications and references cited herein are expresslyincorporated herein by reference in their entirety.

1. A spinal stabilization device, comprising: a central spacer havingfirst and second opposed lateral sides, the central spacer being adaptedto be positioned between posterior elements of adjacent superior andinferior vertebrae and adapted to limit extension of the adjacentsuperior and inferior vertebrae; a first pair of arms having a unitaryconfiguration and extending from the first lateral side of the centralspacer, the first pair of arms being adapted to couple to adjacentsuperior and inferior vertebrae; and a second pair of arms having aunitary configuration and extending from the second lateral side of thecentral spacer, the second pair of arms being adapted to couple toadjacent superior and inferior vertebrae; wherein at least a portion ofat least one of the first and second pair of arms is pliable forproviding resistance to movement of adjacent superior and inferiorvertebrae coupled thereto, and wherein the first and second pair of armsare independently removably mated to the central spacer.
 2. A spinalstabilization device, comprising: an elongate central spacer havingfirst and second opposed lateral sides and having a height at amid-portion that is less than a height at the opposed lateral sides, thecentral spacer being adapted to be positioned between posterior elementsof adjacent superior and inferior vertebrae and adapted to limitextension of the adjacent superior and inferior vertebrae; a first pairarms extending from the first lateral side of the central spacer andadapted to couple to adjacent superior and inferior vertebrae; and asecond pair of arms extending from the second lateral side of thecentral spacer and adapted to couple to adjacent superior and inferiorvertebrae; wherein the first pair of arms comprises a first arm and asecond arm, and the second pair of arms comprises a third arm and afourth arm, and wherein the first, second, third, and fourth arms areindependently removably mated to the central spacer.
 3. The spinalstabilization device of claim 2, wherein the central spacer includes afirst opening formed in the first lateral side and adapted to removablyreceive the first and second arms, and a second opening formed in thesecond, opposed lateral side and adapted to removably receive the thirdand fourth arms.
 4. The spinal stabilization device of claim 3, whereinthe central spacer includes first and second locking mechanisms adaptedto be disposed through the first and second openings for locking thefirst, second, third, and fourth arms to the central spacer.